[Truffle] Warn if using isModuleFunction on a Class.

* In Ruby it should even be a NoMethodError.

Author: eregon

truffle/src/main/java/org/jruby/truffle/nodes/core/CoreMethodNodeManager.java

@@ -93,6 +93,9 @@ private static void addMethod(RubyClass rubyObjectClass, MethodDetails methodDet
             if (anno.onSingleton()) {
                 System.err.println("WARNING: Either onSingleton or isModuleFunction for " + methodDetails.getIndicativeName());
             }
+            if (!module.isOnlyAModule()) {
+                System.err.println("WARNING: Using isModuleFunction on a Class for " + methodDetails.getIndicativeName());
+            }
         }
 
         // Do not use needsSelf=true in module functions, it is either the module/class or the instance.

truffle/src/main/java/org/jruby/truffle/nodes/core/EncodingConverterNodes.java

@@ -114,7 +114,7 @@ public RubyNilClass initialize(RubyEncodingConverter self, RubyString source, Ru
 
     }
 
-    @CoreMethod(names = "search_convpath", isModuleFunction = true, needsSelf = false, required = 2)
+    @CoreMethod(names = "search_convpath", onSingleton = true, required = 2)
     public abstract static class SearchConvPathNode extends CoreMethodNode {
 
         public SearchConvPathNode(RubyContext context, SourceSection sourceSection) {